1. Field of the Invention
The present invention relates to an improved pressure-operated switch for a high-voltage interrupting module. More specifically, the present invention relates to an improvement of the switches disclosed in commonly assigned U.S. Pat. No. 4,342,978, issued Aug. 3, 1982 in the name of Meister, and U.S. Pat. No. 4,370,531, issued Jan. 25, 1983 in the name of Tobin, and in the following commonly assigned U.S. patent applications: Ser. No. 179,367, filed Aug. 18, 1980 (now abandoned in favor of continuation application Ser. No. 550,201, filed Nov. 9, 1983) in the name of Jarosz and Panas; Ser. No. 179,366, filed Aug. 18, 1980 (now abandoned in favor of continuation application Ser. No. 539,396, filed Oct. 6, 1983) in the name of O'Leary, and Ser. No. 437,925, which issued Jan. 24, 1984 as U.S. Pat. No. 4,427,963, and Ser. No. 437,926, both filed Nov. 1, 1982 in the names of Jarosz and Panas.
2. Prior Art
The above patents and patent applications all relate to various aspects of a pressure-operated switch and to a high-voltage interrupting module containing the switch. The switch includes a pair of contacts, which are normally electrically interconnected by direct abutment therebetween or, preferably, by interconnecting them with a shearable or tearable metallic disc or membrane. In preferred embodiments of the switch, one of the contacts is stationary, while the other is movable, although both may be movable. The contacts are separable along a fixed line of direction to open a gap therebetween, thereby opening the switch. One of the contacts, preferably the stationary contact, contains a bore which, in conjunction with a piston or trailer, defines a closed chamber. The chamber houses a power cartridge or similar pressure-generating device.
The switch may be in electrical shunt with a fuse, a fusible element of which, as well as the switch, are preferably housed within a common housing. When the switch is closed (when the contacts thereof are electrically interconnected), the resistance of the current path through the switch is much lower than resistance of the current path through the fusible element, and, accordingly, a majority of the current flowing through the module flows through the switch. In this way, the module has a very high continuous current rating. Upon opening the switch, current is rapidly commutated therefrom to the fusible element where the current is interrupted. Separation of the contacts is achieved by igniting the power cartridge, which evolves high pressure within the chamber. This high pressure acts against the piston and the forces produced thereby rapidly move the piston to rapidly drive the movable contact away from the stationary contact, breaking the normal electrical interconnection and opening the switch. The power cartridge may be ignited in response a trigger signal produced by apparatus which senses a fault current or other over-current in a circuit in which the interrupting module is connected for protection thereof. The trigger-signal-producing apparatus may be that which is disclosed in commonly assigned U.S. patent applications, Ser. Nos. 506,942; 506,943; and 506,944, all filed June 22, 1983 in the name of Ruta.
Specific embodiments of the switch include a second stationary contact having a bore lined with an insulative sleeve. The movable contact is a conductive member covered with an insulative sleeve. When the movable contact is driven away from the first stationary contact, a second disc, which normally interconnects the movable and second stationary contact, is sheared, and the movable contact is telescoped into the second stationary contact producing a second gap therebetween.
The movable contact and the piston move away from the first stationary contact and through a passageway of an insulative liner. Both the movable contact and the piston are received by the passageway in the liner to physically isolate the movable contact from the ignition products of the power cartridge. This isolation prevents or suppresses the formation of any arc between the separating contacts and between the stationary contacts. In preferred embodiments of the switch, the stationary contacts and the liner are engageably surrounded, and have their relative positions fixed, by an insulative housing, which maintains the stationary contacts and the liner in end-to-end abutment with the bores and the passageway axially aligned.
Federal and state shipping regulations require that products such as the above described switch--products containing power cartridges, or similar ignitable devices--remain integral or "self contained" when subjected to a variety of conditions including fire. Tests of early versions of the above-described switch, wherein the insulative housing was cemented or adhered to the stationary contacts and the liner, showed that the heat of an external fire might, in some cases, degrade the cement or adhesive, as well as effect ignition of the power cartridge. The pressure build up within the switch following power cartridge ignition and the degradation of the cement or adhesive might, it was found, result in the stationary contacts being forced out of and separating from the housing. Obviation of the separation of the stationary contact from the housing is a primary object of the present invention.